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Relative change. In any quantitative science, the terms relative change and relative difference are used to compare two quantities while taking into account the "sizes" of the things being compared, i.e. dividing by a standard or reference or starting value. [1] The comparison is expressed as a ratio and is a unitless number.
Fold change. Fold change is a measure describing how much a quantity changes between an original and a subsequent measurement. It is defined as the ratio between the two quantities; for quantities A and B the fold change of B with respect to A is B / A. In other words, a change from 30 to 60 is defined as a fold-change of 2.
Decibel. The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel ( B ). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a power ratio of 10 1/10 (approximately 1.26) or root-power ratio of 10 1/20 (approximately 1.12 ).
The condition number is derived from the theory of propagation of uncertainty, and is formally defined as the value of the asymptotic worst-case relative change in output for a relative change in input. The "function" is the solution of a problem and the "arguments" are the data in the problem. The condition number is frequently applied to ...
Relative density ( ) or specific gravity ( ) is a dimensionless quantity, as it is the ratio of either densities or weights. where is relative density, is the density of the substance being measured, and is the density of the reference. (By convention , the Greek letter rho, denotes density.) The reference material can be indicated using ...
Time dilation. Time dilation is the difference in elapsed time as measured by two clocks, either because of a relative velocity between them ( special relativity ), or a difference in gravitational potential between their locations ( general relativity ). When unspecified, "time dilation" usually refers to the effect due to velocity.
The laws of physics are the same for all observers in any inertial frame of reference relative to one another (principle of relativity). The speed of light in vacuum is the same for all observers, regardless of their relative motion or of the motion of the light source. The resultant theory copes with experiment better than classical mechanics.
The relative velocity, denoted (also or ), is the velocity vector of an object or observer B in the rest frame of another object or observer A . The relative speed is the vector norm of the relative velocity.